1. Field of the Invention
The invention relates to a flat cable, and more particularly to a twist flat cable comprising parallel portions respectively provided alternately with twisted pair portions in the longitudinal direction of the cable, the parallel portion comprising insulated core wires fused to each other, the twisted pair portion comprising twisted pairs each composed of two separately insulated core wires twisted together and being laminated by at least one tape.
2. Prior Art
Flat cables have advantages including the elimination of the need to provide bundle wires and easy wiring due to high flexibility. By virtue of these advantageous, flat cables are utilized in internal wiring of electronic equipment such as personal computers and communication equipment. FIGS. 8 to 14 show conventional flat cables of such a type that parallel portions each comprising insulated core wires fused to each other are respectively provided alternately with twisted pair portions each comprising twisted pairs each composed of two separately insulated core wires twisted together and being laminated in such a manner that the twisted pair portion is sandwiched between two tapes.
FIG. 8 is a plan view of a conventional flat cable, FIG. 9 an enlarged cross-sectional view taken on line IXxe2x80x94IX of FIG. 8, and FIG. 10 an enlarged cross-sectional view taken on line Xxe2x80x94X of FIG. 8. A conventional flat cable 20 comprises parallel portions 1 respectively provided alternately with twisted pair portions 2 in the longitudinal direction of the cable. The parallel portion 1 comprises a plurality of insulated core wires aligned parallel to each other and fused to each other. The twisted pair portion 2 comprises twisted pairs each composed of two separately insulated core wires 6 twisted together. The twisted pair portion 2 is laminated in such a manner that two pressure-sensitive adhesive tapes or thermally fusible tapes 3 are disposed respectively on the upper and lower portions of the twisted pair portion 2 so as to sandwich the twisted pair portion 2 therebetween. The insulated core wire 6 comprises a conductor 4 and an insulation 5 covering the circumference of the conductor 4.
FIGS. 11 to 14 show another example of the conventional flat cable. FIG. 11 is a plan view (a surface view), FIG. 12a bottom view (a backside view), FIG. 13 an enlarged cross-sectional view taken on line XIIIxe2x80x94XIII of FIG. 11, and FIG. 14 an enlarged cross-sectional view taken on line XIVxe2x80x94XIV of FIG. 11.
This conventional flat cable 20a comprises parallel portions 1 respectively provided alternately with twisted pair portions 2. The parallel portion 1 comprises a plurality of insulated core wires 6 aligned parallel to each other and fused to each other. The twisted pair portion 2 comprises twisted pairs each composed of two separately insulated core wires 6 twisted together. One pressure-sensitive adhesive tape or thermally fusible tape 3b is laminated onto one side of the cable over the whole length in the longitudinal direction of the cable, and one pressure-sensitive adhesive tape or thermally fusible tape 3 is laminated onto the other side of the twisted pair portion 2.
According to the flat cable having twisted pair portions laminated by tapes, the upper and lower portions of each of the twisted pair portions are respectively fixed onto two pressure-sensitive adhesive tapes or thermally fusible tapes. Therefore, there is a fear that, when the twisted pair portion is bent, the insulated core wire at the twisted pair end (including the side portion of the cable) is separated and is projected. Further, strictly speaking, the projection of the twisted pair portion poses a problem that the electrical characteristics of the projected twisted pair portion would be deteriorated. In addition, in the conventional flat cable having the laminated twisted pair portions, pressure-sensitive adhesive plastic tapes or thermally fusible plastic tapes are used for the lamination. This poses a problem that the interior of electronic equipment is adversely affected by noise caused by peripheral devices and, in some cases, satisfactorily stable transmission characteristics cannot be provided.
Accordingly, it is an object of the invention to provide a flat cable which, when bent, can prevent the separation or projection of twisted pair at the twisted pair end and thus can maintain the appearance of the whole cable.
It is another object of the invention to provide a flat cable which does not have any adverse effect on the transmission characteristics of the twisted pair portions.
It is a further object of the invention to reduce the adverse effect of noise caused by peripheral devices on the interior of electronic equipment.
According to the first feature of the invention, a flat cable comprises parallel portions respectively provided alternately with twisted pair portions in the longitudinal direction of the flat cable, said parallel portion comprising a plurality of insulated core wires aligned parallel to each other and fused to each other, said twisted pair portion comprising twisted pairs each composed of two separately insulated core wires twisted together,
said twisted pair portion in its surface, backside, and left and right side faces being surrounded by at least one tape.
According to the second feature of the invention, a flat cable comprises parallel portions respectively provided alternately with twisted pair portions in the longitudinal direction of the flat cable, said parallel portion comprising a plurality of insulated core wires aligned parallel to each other and fused to each other, said twisted pair portion comprising twisted pairs each composed of two separately insulated core wires twisted together, a pressure-sensitive adhesive tape being laminated onto one side of the cable over the whole length of the cable in the longitudinal direction,
said twisted pair portion in its surface, backside, and left and right side faces being surrounded by at least one tape.
In the flat cables according to the first and second features of the invention, the tape may be any one of a pressure-sensitive adhesive tape, a thermally fusible tape, a pressure-sensitive adhesive shield tape, and a thermally fusible shield tape.
According to the above construction, even when the flat cable is bent, the separation or projection of twisted pair at the twisted pair end can be prevented and, thus, the appearance of the whole cable can be maintained. Further, by virtue of the prevention of the separation or projection of the twisted pair, stable transmission characteristics can be maintained at the twisted pair portions. Further, when the pressure-sensitive adhesive shield tape is used, the adverse effect of noise caused by peripheral devices on the interior of electronic equipment can be reduced.